1. Field of the Invention
This invention relates to an optical device that transforms a spatially, nonuniform laser beam into a spatially homogeneous profile suitable for precision micromachining with a laser or as an illumination source for a projection system.
2. Description of the Prior Art
U.S. Pat. No. 4,733,944 discloses a pair of crossed lenticular cylindrical lens structures coupled with a focusing lens. The total number of optical surfaces is ten (10). If a UV excimer laser is being homogenized, this number of surfaces represents a significant source of losses and costs in construction of the homogenizer. Moreover, the number of lens elements requires careful and precise alignment of the laser beam in relation to all of the optics comprising the homogenizer, in particular angular rotation of the lenslets and how they are positioned along the X and Y plane of the optical axis.
Lenticular lens arrays have been used for decades as illumination systems for TVs, projectors and other illumination devices, as disclosed in U.S. Pat. Nos. 2,326,970 and 2,531,399. They tend to have poor optical efficiency and are difficult to fabricate, especially for use in the ultraviolet spectrum.
The known prior art lens arrays include large numbers of optical components to create a homogenized spatial distribution of light in space as an illumination source for laser machining, a lithographic illuminator or as an integrator for any type of projection system. The known devices are unable to create a homogenized ring illumination to accommodate a greater number of illumination applications such as for microelectronic devices such as memory modules, multichip modules and the like.
Prior art homogenizers typically require a condenser with a focal length of one meter (1 m) plus the length needed for two pairs of crossed cylindrical lenses. A prior art homogenizer therefore has a focal length of about one and a half meters (1.5 m).
There is therefore a need for a homogenizer having a substantially shorter focal length.
However, in view of the prior art taken as a whole at the time the present invention was made, it was not obvious to those of ordinary skill how the identified needs could be fulfilled.